We mapped – for the first time – the probability of occurrence of drought over Spain, with the overriding aim of improving current drought assessment, management and mitigation measures and strategies across the region. We employed two well-established drought indices: the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI). Drought characteristics (i.e. duration and severity) were characterised at 1-, 3-, 6- and 12-month, implying that drought event is attained only when the index values are lower than zero. We applied the extreme value theory to map drought hazard probability. Following this procedure, we tested different thresholds to generate the peak-over-threshold drought severity and magnitude series, besides evaluating different three-parametric distributions and thresholds to fit these series. Our results demonstrate that the Generalized Pareto distribution performs well in estimating the frequencies of drought magnitude and duration, with good agreement between the observed and modelled data when using upper percentiles to generate the peak-over-threshold series. Spatially, our estimations suggest a higher probability of extreme drought events in southern and central areas of Spain, compared to northern and eastern regions. Nevertheless, there are strong differences in drought probability estimations between drought indices (i.e. SPI and SPEI), as well as among drought timescales.

Sponsorship :

This work was supported by the research projects CGL2014-52135-C03-01 and PCIN-2015-220 financed by the Spanish Commission of Science and Technology and FEDER, 1560/2015: Herramientas de monitorización de la vegetación mediante modelización ecohidrológica en parques continentales financed by the Red de Parques Nacionales, IMDROFLOOD financed by the Water Works 2014 co-funded call of the European Commission and INDECIS, which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by MINECO with co-funding by the European Union 30 (Grant 690462).